With the development of broadband telecommunication systems, the use of data channels to carry voice signals is becoming widespread. The voice signals may be transmitted over a variety of medium and employing different protocols. For instance, the transfer of voice signals has become increasingly ubiquitous, employing a vast array of technologies such as Digital Subscriber Line Service and over a vast array of networks such as Internet Protocol based packet networks. Moreover, there is every reason to believe that this trend will continue.
One measurement of an efficiency associated with a signal traversing a communications channel of a telecommunications network is the bit error rate (BER). The BER may be defined as the percentage of received bits having errors relative to the total number of bits received during a transmission. Generally speaking, the BER associated with the transmission of voice signals is about 10−3 and of non-voice data signals about 10−7. Thus, data signals are typically more sensitive to errors than voice signals. Although voice and data signals have different BER tolerances and sensitivity levels, voice and data signals have been processed in the same manner in telecommunication systems of the past, at least insofar as the requirements associated with the BER are concerned. While the telecommunications systems presently employed are less complex to implement, requiring voice signals and data signals to abide by equivalent transport techniques (even though the requirements may be different) is not the most efficient use of the bandwidth of a telecommunications network.
In conjunction with the transfer of information across the telecommunications network, telecommunications systems often employ modulation techniques to more efficiently transfer the information across a communications channel of the network. For instance, quadrature amplitude modulation (QAM) is one modulation technique that carries the information bits in both the in-phase and quadrature direction and shifts the signal band around a single carrier frequency. In a modulation technique such as QAM, the unit of information transferred is called a “symbol”, which may in turn represent multiple bits of information. The number of bits represented by a symbol is referred to as its “symbol density.”
A theoretical channel capacity of a communications channel associated with a telecommunications network can be derived by the well recognized Shannon's formula. While Shannon's theorem describes the theoretical capacity of a communications channel, for a given modulation technique there is a disparity between the attainable channel capacity and the theoretical capacity. The difference between the theoretical and attainable channel capacity is represented by the signal-to-noise ratio (SNR) gap and it determines how many bits can be loaded to a symbol for a particular modulation technique such as QAM.
Additionally, for reasons that will become more apparent, the SNR gap is related to the BER associated with the information traversing the communications channel and, as mentioned above, has a bearing on the maximum symbol constellation density allowable. In a situation where the SNR gap is quite large, each transmitted symbol conveys less information to accommodate the larger gap. (i.e., the attainable channel capacity is further removed from the theoretical channel capacity.) Thus, it is important to pack as much information as possible into a symbol (or for that matter any representation of information traversing a communications channel) to more effectively maximize the bandwidth of the telecommunications network.
Accordingly, what is needed in the art is a system and method that more efficiently manages the transmission of information (e.g., voice and data signals) across a telecommunications network that overcomes the deficiencies in the prior art.